Effect of calcination temperature on microstructure and photocatalytic activity of BiOX (X=Cl, Br)

A series of BiOX (X=Cl, Br) were prepared by simple hydrolysis and then calcined at various temperatures and they were characterized by XRD, Raman, SEM, DSC–TGA, BET and UV–Vis. The photocatalytic activity was evaluated by photocatalytic degradation of methyl orange (MO) solution under simulated solar light irradiation. The results show that the phase structure, crystallite size, morphology, specific surface area, porous structure, and the absorption band-edges are related to the calcination temperature. For BiOBr, it has completely transformed to Bi24O31Br10 at 600 °C and begins to transform to Bi2O3 at 800 °C. As for BiOCl, it begins to transform to Bi24O31Cl10 at 600 °C and completely transforms to Bi24O31Cl10 at 800 °C. Finally, the photocatalytic activity of BiOCl decreases with the temperature increasing owing to decrease of the specific surface areas and pore size, while the photocatalytic activity of BiOBr increases in the first stage and then decreases, which is related to good crystallization and three-dimensional structure.